When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted engine emissions, such as oxides of nitrogen, e.g., NOx. One conventional way of reducing such unwanted emissions is to direct some of the exhaust gas produced by the engine back into the air charge that will be combusted by the engine via a so-called exhaust gas recirculation (EGR) system.
In conventional EGR systems EGR mass flow rate may typically be estimated as a function of the square root of an average delta pressure across a flow restriction orifice in-line with an EGR conduit connected between the exhaust manifold and the intake manifold of the engine. Under steady state, e.g. constant, EGR flow conditions the conventional EGR flow rate estimation technique can produce accurate results. However, under transient engine operating conditions inaccuracies arise in the conventional EGR mass flow rate estimation process just described due to the pulsating nature of EGR flow under such transient operating conditions. Under such transient operating conditions, the average value of the EGR mass flow rate cannot be accurately computed from the average delta pressure value due to the inherent non-linearity associated with the square root term. It is accordingly desirable to be able to estimate instantaneous mass flow rates of exhaust gas through such an EGR system for more accurate diagnostic and/or engine control purposes.